Add `src/main/liberty` and `src/test/liberty` to the list of java source folders

[lmsurpre]

I think it would be helpful for the Liberty Tools to add these folders to the list of project source folders.

The Maven plugin (m2e) does something similar for src/main/resources and src/test/resources.
Its a little thing, but its makes those appear right under the project in the Explorer views so that users don't need to drill into the src folder hierarchy.

[lmsurpre]

Actually, on second thought, maybe that is really just for files that will generate output that should be on the classpath... feel free to close or change into a story like "feature the liberty maven tools artifacts higher in the tree"